This invention relates to a method of storing heavy hydrocarbon oil and a vessel used therefor, in which heavy hydrocarbon oil, for example, crude oil having a high pour point is normally stored in the vessel in a state solidified at the environmental temperature and is heated to be fluidized when required so that it can be conveniently delivered from the vessel.
Various kinds of tanks including a cone roof tank, a floating tank and a dome tank are generally used for the storage of liquid hydrocarbons such as crude oil and heavy oil. However, liquid hydrocarbons containing high-molecular paraffin, wax, etc. in large amounts and having a high pour point, for example, crude oil produced at Minas in Indonesia, crude oil produced at Taiching in China, crude oil produced in Africa, etc. have such a property that they solidify at the atmospheric temperature. According to the prior art practice for storing such heavy hydrocarbon oil in a storage tank, heat has been continuously applied to the oil in the storage tank so as to raise the temperature of the oil up to a level of, for example, 60.degree. C. which is higher by about 15.degree. C. than the pour point, and for this purpose, a bottom heater for steam heating has invariably been installed in the bottom of any one of the tank types including the cone roof tank, floating tank and dome tank. However, even when the entire side wall of such a tank is provided with lagging means for thermal insulation, a large quantity of heat necessarily dissipates to the exterior from the tank side wall occupying a large proportion of the tank surface area, resulting in a high maintenance cost. Further, the problems of liberation of air-polluting gases and deposition of sludge have been unavoidable due to the fact that the oil is stored in its liquid form. Therefore, the storage of the crude oil having such a high pour point has required a higher cost than that having a low pour point and has not been beneficial from the economical standpoint in spite of the fact that such crude oil has a higher caloric value and includes a smaller amount of sulphur.
On the other hand, the aforementioned crude oil containing wax and like components in large amounts and having the high pour point has such a notable property that it shows no fluidity once it solidifies and remains in that state unless heat is applied thereto. Therefore, the crude oil would not leak or flow out of the storage tank even when a crack, a crevice or the like may be developed in the tank side wall or bottom, and even in the event of partial or serious destruction of the storage tank, it would not percolate into the ground in a large amount and can be easily cleared compared with the liquid hydrocarbons, since it is stored in the solidified form. Further, even in the event of flowout from the tank onto the sea, the crude oil of solidified form floats on the surface of the sea so that it can be easily handled or removed and would not contaminate the sea by diffusing along the surface of the sea. Therefore, the storage of the crude oil of this kind in its solidified state is advantageous from the standpoints of prevention of environmental pollution and danger compared with liquid hydrocarbons having a low pour point, and such crude oil is especially suitable for the purpose of storage of a huge amount of oil of this kind over a long period of time.